There are many applications where it is desirable to transfer power without a physical connection between the power supply and the power load.
For example, for rotating machinery, power connections between the rotating parts and the stationary parts are typically made using slip rings. However, these are subject to wear and thus have maintenance requirements. There is therefore a need to be able to provide a contactless power transfer system.
There are also applications where a physical barrier exists to the passage of cables. For example, providing underwater lighting on the external surface of a boat hull, or within a tank, is desirably carried out without passing electricity supply cables through the hull or tank, since the integrity of the hull or tank needs to be maintained. Running external cables down the side of the hull is visually unacceptable, so it has been proposed to supply power inductively through the hull to externally mounted lights. However, power transmission depends very much on the thickness and materials of the hull, and so each installation has to be specifically designed for the particular boat and position of the light on the boat. Additionally, control of the external lights, for example to vary brightness, is difficult.
JP2002251901 discloses an underwater lighting system for which power is supplied inductively.
WO2010080737 discloses a RFID communication system which is configured to handle variations in the delivery of power to a remote device resulting from relative movement of the remote device and the inductive power supply. In one embodiment the remote device toggles between load configurations to communicate with the inductive power supply. A sensor in the remote device detects a characteristic of power in the remote device and configures the communication load based on the sensor output. In another embodiment, the remote device adjusts the dynamic communication load configuration in the remote device in response to a failure to receive a response from the inductive power supply.
WO2011036343 discloses a method of wirelessly powering a load over an inductive link, in which data is transmitted relating to the output voltage and/or current from a secondary side to a primary side through an inductive power link to regulate the output of an inductive power supply.